1. Field of the Invention
This invention relates to sound analysis and in particular to a method and apparatus for quantitatively measuring and analyzing sound characteristics in phonographic-type record discs.
2. Brief Description of the Prior Art
Most phonographic-type record discs are presently made from a tape, e.g., a magnetic tape used to initially record the desired sounds for reproduction and this recording on the tape typically takes place in a sound recording studio. Thereafter, the tape may be used to produce a master record disc. In producing a master record disc, elecrical signals representative of these sounds on the tape are used to vibrate a cutting tool which cuts a groove into the base material or so-called "lacquer" used to ultimately form the master record disc, and which lacquer is typically formed of a nitrocellulose material.
In order to form the master, the so-called "lacquer" is then plated, e.g., by spraying or the like with a conductive metal such as silver. The silver coated lacquer is then dipped into a nickle bath to form a nickle plating. The nickle plating is peeled off and this plating constitutes, the record disc master since it contains grooves representative of the sounds generated from the tape.
The master record disc, which is used to generate the so-called "mother", contains grooves which are a positive of the sounds on the record tape and thus, any reproduction from them other would produce a record disc containing a negative form of the sounds. Accordingly, the mother is plated in a manner as previously described, and this plating when removed contains a negative of the sounds on the recorded tape. This latter plating often referred to as a "stample" is used to produce copies of record discs in a conventional record disc producing press. In some cases the steps of producing the master and the mother are eliminated and the stample may be produced directly from the lacquer, in which case the stample is sometimes referred to as the master record disc.
Generally, the phonographic disc, usually polyvinyl chloride, does not hold an exact shape when it is pressed. Usually, the disc holds the shape associated with most frequencies, but it may not hold the shape peculiar to certain frequencies. Thus, the phonographic record disc may not be able to accurately reproduce the entire original sound wave. Specifically, the record exhibits a loss or a distortion in the reproduction of certain frequencies.
A certain amount of surface noise is associated with all record materials. This noise is characteristic of the particular material and, hence, the sound qualities, such as loudness, differ from one material to the next. Other noises may be produced by the record which are independent of this surface noise. These other noises may be randomly dispersed high decibel levels, which can result from imperfections in the record surface, such as those caused by voids or contaminants. The voids and contaminants might be introduced in any of the steps which take place during fabrication of the master or stample itself or they may be later introduced during molding of the disc. It is, of course, desirable to be able to differentiate the sources of the noise in order to determine the best steps to minimize or eliminate them.
The record discs fabricated from different materials have different reproduction characteristics and capabilities. Some materials may not be capable of accurately reproducing all of the audible frequencies. Hence, in evaluating materials for phonographic discs, it is necessary to take into consideration, not only the surface noise level, and the ease with which voids and contaminants; may be minimized, but also the reproduction characteristics of the material.
Digital frequency analyzers have been used in connection with computers for making vibration analysis. This type of system is frequently employed to analyze and study vibrations in certain equipment. This type of system has also been used to predict and study earthquakes In addition, microphones have been used to inroduce signals into a digital frequency analyzer which generates wave forms in response to the signals introduced. Further, frequency analyzers have been used in equalizing the sound across "sound rooms", e.g., rooms environmentally isolated to hear certain sounds created therein, in order to eliminate or compensate for reverberations and the like.
Heretofore, none of these systems have been used for or capable of effectively analyzing signals made by phonographic record discs to determine the reproduction capabilities of the material or to quantify surface noise levels separately from other noise levels. In addition, none of the prior art systems thus configured has been able to analyze sound waves generated by phonographic record discs to discover the causes of high level noise areas on the discs or to quantify such high level noise on record discs.